WASHINGTON ― Russia‘s prime minister approved Thursday the deployment of Russian warplanes to a disputed island off the northeast coast of Japan, Reuters reports.

The Russian Defence Ministry plans to sue one of the civilian airstrips on the island of Iturup ― or Etorofu, as it is called in Japan ― to base its aerial forces.

The island is one of four seized by the Soviets at the end of World War II. The disagreement over ownership of the small island chain is so visceral that the two countries have not signed an official treaty denoting the end of the war.

Russian Sukhoi Su-30SM jets land Oct. 3, 2015, on a runway at the Hmeimim airbase in the Syrian province of Latakia. (Komsomolskaya Pravda/AFP)
Russian Sukhoi Su-30SM jets land Oct. 3, 2015, on a runway at the Hmeimim airbase in the Syrian province of Latakia. (Komsomolskaya Pravda/AFP)

“We believe this could result in Russia’s military power being strengthened on the four islands and that contradicts Japan’s position on the islands,” said a statement released by the Japanese Embassy in Moscow.

An unnamed source cited in Russian daily Kommersant said the planes will temporarily be deployed on the island.

The deployment would likely further strain relations between Moscow and Tokyo, which has become increasingly tense due to Japan’s decision to deploy U.S. Aegis Ashore missile defense systems in the Akita and Yamaguchi prefectures.

While ostensibly procured to mitigate the growing ballistic missile threat from North Korea, which shot two missiles over Japan’s Hokkaido prefecture last year, Russia and China are concerned the U.S. missile systems are also intended to hedge against their own missile capabilities.

Japan was recently cleared by the U.S. State Department to purchase four Standard Missile-3 Block IIA interceptors. The interceptors can be loaded into the Mark 41 Vertical Launch System used on Aegis destroyers and Aegis Ashore.

Japan is one of five non-U.S. countries that operate the Aegis Combat System, fitting the system to its Kongo- and Atago-class guided-missile destroyers.